This invention relates to the art of cleaning aluminum surfaces. More particularly, it relates to the art of cleaning aluminum surfaces which have been previously subjected to cold forming operations during which organic lubricants are applied to the aluminum surface, a residue of which remains on the surface after forming is completed.
Metal surface cleaning is essential to the efficacy of many metal finishing operations. Thoroughly cleaned surfaces are much more receptive to subsequent corrosion preventive treatments and the application of organic finishes. Cleaning is especially important in the case of aluminum surfaces which have been cold formed such as drawn and ironed aluminum cans.
In accordance with current procedures for manufacturing aluminum cans, circular blanks are stamped from aluminum sheet. The blanks are then formed into cups with a suitable die or cupping press and the thus-formed cups are then drawn or ironed in one or more stages to form the cup into a can of the desired dimensions. Normally these forming operations are assisted and the dies and metallic surface protected by the application of lubricants to the surface prior to or during the forming operations. As a result of this manufacturing process, the fully-formed can contains residual quantities of the organic lubricant on the surface and in addition contains metallic particles called smut which are formed on the can surface as a result of the drawing operation. It is essential that the residual lubricant and smut be removed from the surface prior to further treatment.
Conventional techniques for cleaning such aluminum surfaces employ both alkaline and acidic aqueous solutions. Such solutions are typically operated at a temperature of from 180.degree. to 210.degree.F in order to obtain adequate cleaning within a reasonable period of time. The conventional acidic solutions may contain, in addition to an acidic component, a hexavalent chromium compound, a fluoride accelerating compound, and a surfactant. To date, however, it has not been found possible to clean such surfaces through the use of an energy-saving low-temperature solution.